text: /*
   * IPv6 fragment reassembly for connection tracking
   *
   * Copyright (C)2004 USAGI/WIDE Project
   *
   * Author:
   *	Yasuyuki Kozakai @USAGI <yasuyuki.kozakai@toshiba.co.jp>
   *
   * Based on: net/ipv6/reassembly.c
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   */
  
  #define pr_fmt(fmt) "IPv6-nf: " fmt
  
  #include <linux/errno.h>
  #include <linux/types.h>
  #include <linux/string.h>
  #include <linux/socket.h>
  #include <linux/sockios.h>
  #include <linux/jiffies.h>
  #include <linux/net.h>
  #include <linux/list.h>
  #include <linux/netdevice.h>
  #include <linux/in6.h>
  #include <linux/ipv6.h>
  #include <linux/icmpv6.h>
  #include <linux/random.h>
  #include <linux/slab.h>
  
  #include <net/sock.h>
  #include <net/snmp.h>
  #include <net/ipv6_frag.h>
  
  #include <net/protocol.h>
  #include <net/transp_v6.h>
  #include <net/rawv6.h>
  #include <net/ndisc.h>
  #include <net/addrconf.h>
  #include <net/inet_ecn.h>
  #include <net/netfilter/ipv6/nf_conntrack_ipv6.h>
  #include <linux/sysctl.h>
  #include <linux/netfilter.h>
  #include <linux/netfilter_ipv6.h>
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <net/netfilter/ipv6/nf_defrag_ipv6.h>
  
  static const char nf_frags_cache_name[] = "nf-frags";
  
  static struct inet_frags nf_frags;
  
  #ifdef CONFIG_SYSCTL
  
  static struct ctl_table nf_ct_frag6_sysctl_table[] = {
  	{
  		.procname	= "nf_conntrack_frag6_timeout",
  		.data		= &init_net.nf_frag.frags.timeout,
  		.maxlen		= sizeof(unsigned int),
  		.mode		= 0644,
  		.proc_handler	= proc_dointvec_jiffies,
  	},
  	{
  		.procname	= "nf_conntrack_frag6_low_thresh",
  		.data		= &init_net.nf_frag.frags.low_thresh,
  		.maxlen		= sizeof(unsigned long),
  		.mode		= 0644,
  		.proc_handler	= proc_doulongvec_minmax,
  		.extra2		= &init_net.nf_frag.frags.high_thresh
  	},
  	{
  		.procname	= "nf_conntrack_frag6_high_thresh",
  		.data		= &init_net.nf_frag.frags.high_thresh,
  		.maxlen		= sizeof(unsigned long),
  		.mode		= 0644,
  		.proc_handler	= proc_doulongvec_minmax,
  		.extra1		= &init_net.nf_frag.frags.low_thresh
  	},
  	{ }
  };
  
  static int nf_ct_frag6_sysctl_register(struct net *net)
  {
  	struct ctl_table *table;
  	struct ctl_table_header *hdr;
  
  	table = nf_ct_frag6_sysctl_table;
  	if (!net_eq(net, &init_net)) {
  		table = kmemdup(table, sizeof(nf_ct_frag6_sysctl_table),
  				GFP_KERNEL);
  		if (table == NULL)
  			goto err_alloc;
  
  		table[0].data = &net->nf_frag.frags.timeout;
  		table[1].data = &net->nf_frag.frags.low_thresh;
  		table[1].extra2 = &net->nf_frag.frags.high_thresh;
  		table[2].data = &net->nf_frag.frags.high_thresh;
  		table[2].extra1 = &net->nf_frag.frags.low_thresh;
  		table[2].extra2 = &init_net.nf_frag.frags.high_thresh;
  	}
  
  	hdr = register_net_sysctl(net, "net/netfilter", table);
  	if (hdr == NULL)
  		goto err_reg;
  
  	net->nf_frag_frags_hdr = hdr;
  	return 0;
  
  err_reg:
  	if (!net_eq(net, &init_net))
  		kfree(table);
  err_alloc:
  	return -ENOMEM;
  }
  
  static void __net_exit nf_ct_frags6_sysctl_unregister(struct net *net)
  {
  	struct ctl_table *table;
  
  	table = net->nf_frag_frags_hdr->ctl_table_arg;
  	unregister_net_sysctl_table(net->nf_frag_frags_hdr);
  	if (!net_eq(net, &init_net))
  		kfree(table);
  }
  
  #else
  static int nf_ct_frag6_sysctl_register(struct net *net)
  {
  	return 0;
  }
  static void __net_exit nf_ct_frags6_sysctl_unregister(struct net *net)
  {
  }
  #endif
  
  static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb,
  			     struct sk_buff *prev_tail, struct net_device *dev);
  
  static inline u8 ip6_frag_ecn(const struct ipv6hdr *ipv6h)
  {
  	return 1 << (ipv6_get_dsfield(ipv6h) & INET_ECN_MASK);
  }
  
  static void nf_ct_frag6_expire(struct timer_list *t)
  {
  	struct inet_frag_queue *frag = from_timer(frag, t, timer);
  	struct frag_queue *fq;
  	struct net *net;
  
  	fq = container_of(frag, struct frag_queue, q);
  	net = container_of(fq->q.net, struct net, nf_frag.frags);
  
  	ip6frag_expire_frag_queue(net, fq);
  }
  
  /* Creation primitives. */
  static struct frag_queue *fq_find(struct net *net, __be32 id, u32 user,
  				  const struct ipv6hdr *hdr, int iif)
  {
  	struct frag_v6_compare_key key = {
  		.id = id,
  		.saddr = hdr->saddr,
  		.daddr = hdr->daddr,
  		.user = user,
  		.iif = iif,
  	};
  	struct inet_frag_queue *q;
  
  	q = inet_frag_find(&net->nf_frag.frags, &key);
  	if (!q)
  		return NULL;
  
  	return container_of(q, struct frag_queue, q);
  }
  
  
  static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
  			     const struct frag_hdr *fhdr, int nhoff)
  {
  	unsigned int payload_len;
  	struct net_device *dev;
  	struct sk_buff *prev;
  	int offset, end, err;
  	u8 ecn;
  
  	if (fq->q.flags & INET_FRAG_COMPLETE) {
  		pr_debug("Already completed\n");
  		goto err;
  	}
  
  	payload_len = ntohs(ipv6_hdr(skb)->payload_len);
  
  	offset = ntohs(fhdr->frag_off) & ~0x7;
  	end = offset + (payload_len -
  			((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));
  
  	if ((unsigned int)end > IPV6_MAXPLEN) {
  		pr_debug("offset is too large.\n");
  		return -EINVAL;
  	}
  
  	ecn = ip6_frag_ecn(ipv6_hdr(skb));
  
  	if (skb->ip_summed == CHECKSUM_COMPLETE) {
  		const unsigned char *nh = skb_network_header(skb);
  		skb->csum = csum_sub(skb->csum,
  				     csum_partial(nh, (u8 *)(fhdr + 1) - nh,
  						  0));
  	}
  
  	/* Is this the final fragment? */
  	if (!(fhdr->frag_off & htons(IP6_MF))) {
  		/* If we already have some bits beyond end
  		 * or have different end, the segment is corrupted.
  		 */
  		if (end < fq->q.len ||
  		    ((fq->q.flags & INET_FRAG_LAST_IN) && end != fq->q.len)) {
  			pr_debug("already received last fragment\n");
  			goto err;
  		}
  		fq->q.flags |= INET_FRAG_LAST_IN;
  		fq->q.len = end;
  	} else {
  		/* Check if the fragment is rounded to 8 bytes.
  		 * Required by the RFC.
  		 */
  		if (end & 0x7) {
  			/* RFC2460 says always send parameter problem in
  			 * this case. -DaveM
  			 */
  			pr_debug("end of fragment not rounded to 8 bytes.\n");
  			inet_frag_kill(&fq->q);
  			return -EPROTO;
  		}
  		if (end > fq->q.len) {
  			/* Some bits beyond end -> corruption. */
  			if (fq->q.flags & INET_FRAG_LAST_IN) {
  				pr_debug("last packet already reached.\n");
  				goto err;
  			}
  			fq->q.len = end;
  		}
  	}
  
  	if (end == offset)
  		goto err;
  
  	/* Point into the IP datagram 'data' part. */
  	if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data)) {
  		pr_debug("queue: message is too short.\n");
  		goto err;
  	}
  	if (pskb_trim_rcsum(skb, end - offset)) {
  		pr_debug("Can't trim\n");
  		goto err;
  	}
  
  	/* Note : skb->rbnode and skb->dev share the same location. */
  	dev = skb->dev;
  	/* Makes sure compiler wont do silly aliasing games */
  	barrier();
  
  	prev = fq->q.fragments_tail;
  	err = inet_frag_queue_insert(&fq->q, skb, offset, end);
  	if (err) {
  		if (err == IPFRAG_DUP) {
  			/* No error for duplicates, pretend they got queued. */
  			kfree_skb(skb);
  			return -EINPROGRESS;
  		}
  		goto insert_error;
  	}
  
  	if (dev)
  		fq->iif = dev->ifindex;
  
  	fq->q.stamp = skb->tstamp;
  	fq->q.meat += skb->len;
  	fq->ecn |= ecn;
  	if (payload_len > fq->q.max_size)
  		fq->q.max_size = payload_len;
  	add_frag_mem_limit(fq->q.net, skb->truesize);
  
  	/* The first fragment.
  	 * nhoffset is obtained from the first fragment, of course.
  	 */
  	if (offset == 0) {
  		fq->nhoffset = nhoff;
  		fq->q.flags |= INET_FRAG_FIRST_IN;
  	}
  
  	if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
  	    fq->q.meat == fq->q.len) {
  		unsigned long orefdst = skb->_skb_refdst;
  
  		skb->_skb_refdst = 0UL;
  		err = nf_ct_frag6_reasm(fq, skb, prev, dev);
  		skb->_skb_refdst = orefdst;
  
  		/* After queue has assumed skb ownership, only 0 or
  		 * -EINPROGRESS must be returned.
  		 */
  		return err ? -EINPROGRESS : 0;
  	}
  
  	skb_dst_drop(skb);
  	return -EINPROGRESS;
  
  insert_error:
  	inet_frag_kill(&fq->q);
  err:
  	skb_dst_drop(skb);
  	return -EINVAL;
  }
  
  /*
   *	Check if this packet is complete.
   *
   *	It is called with locked fq, and caller must check that
   *	queue is eligible for reassembly i.e. it is not COMPLETE,
   *	the last and the first frames arrived and all the bits are here.
   */
  static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb,
  			     struct sk_buff *prev_tail, struct net_device *dev)
  {
  	void *reasm_data;
  	int payload_len;
  	u8 ecn;
  
  	inet_frag_kill(&fq->q);
  
  	ecn = ip_frag_ecn_table[fq->ecn];
  	if (unlikely(ecn == 0xff))
  		goto err;
  
  	reasm_data = inet_frag_reasm_prepare(&fq->q, skb, prev_tail);
  	if (!reasm_data)
  		goto err;
  
  	payload_len = ((skb->data - skb_network_header(skb)) -
  		       sizeof(struct ipv6hdr) + fq->q.len -
  		       sizeof(struct frag_hdr));
  	if (payload_len > IPV6_MAXPLEN) {
  		net_dbg_ratelimited("nf_ct_frag6_reasm: payload len = %d\n",
  				    payload_len);
  		goto err;
  	}
  
  	/* We have to remove fragment header from datagram and to relocate
  	 * header in order to calculate ICV correctly. */
  	skb_network_header(skb)[fq->nhoffset] = skb_transport_header(skb)[0];
  	memmove(skb->head + sizeof(struct frag_hdr), skb->head,
  		(skb->data - skb->head) - sizeof(struct frag_hdr));
  	skb->mac_header += sizeof(struct frag_hdr);
  	skb->network_header += sizeof(struct frag_hdr);
  
  	skb_reset_transport_header(skb);
  
  	inet_frag_reasm_finish(&fq->q, skb, reasm_data);
  
  	skb->ignore_df = 1;
  	skb->dev = dev;
  	ipv6_hdr(skb)->payload_len = htons(payload_len);
  	ipv6_change_dsfield(ipv6_hdr(skb), 0xff, ecn);
  	IP6CB(skb)->frag_max_size = sizeof(struct ipv6hdr) + fq->q.max_size;
  
  	/* Yes, and fold redundant checksum back. 8) */
  	if (skb->ip_summed == CHECKSUM_COMPLETE)
  		skb->csum = csum_partial(skb_network_header(skb),
  					 skb_network_header_len(skb),
  					 skb->csum);
  
  	fq->q.fragments = NULL;
  	fq->q.rb_fragments = RB_ROOT;
  	fq->q.fragments_tail = NULL;
  	fq->q.last_run_head = NULL;
  
  	return 0;
  
  err:
  	inet_frag_kill(&fq->q);
  	return -EINVAL;
  }
  
  /*
   * find the header just before Fragment Header.
   *
   * if success return 0 and set ...
   * (*prevhdrp): the value of "Next Header Field" in the header
   *		just before Fragment Header.
   * (*prevhoff): the offset of "Next Header Field" in the header
   *		just before Fragment Header.
   * (*fhoff)   : the offset of Fragment Header.
   *
   * Based on ipv6_skip_hdr() in net/ipv6/exthdr.c
   *
   */
  static int
  find_prev_fhdr(struct sk_buff *skb, u8 *prevhdrp, int *prevhoff, int *fhoff)
  {
  	u8 nexthdr = ipv6_hdr(skb)->nexthdr;
  	const int netoff = skb_network_offset(skb);
  	u8 prev_nhoff = netoff + offsetof(struct ipv6hdr, nexthdr);
  	int start = netoff + sizeof(struct ipv6hdr);
  	int len = skb->len - start;
  	u8 prevhdr = NEXTHDR_IPV6;
  
  	while (nexthdr != NEXTHDR_FRAGMENT) {
  		struct ipv6_opt_hdr hdr;
  		int hdrlen;
  
  		if (!ipv6_ext_hdr(nexthdr)) {
  			return -1;
  		}
  		if (nexthdr == NEXTHDR_NONE) {
  			pr_debug("next header is none\n");
  			return -1;
  		}
  		if (len < (int)sizeof(struct ipv6_opt_hdr)) {
  			pr_debug("too short\n");
  			return -1;
  		}
  		if (skb_copy_bits(skb, start, &hdr, sizeof(hdr)))
  			BUG();
  		if (nexthdr == NEXTHDR_AUTH)
  			hdrlen = (hdr.hdrlen+2)<<2;
  		else
  			hdrlen = ipv6_optlen(&hdr);
  
  		prevhdr = nexthdr;
  		prev_nhoff = start;
  
  		nexthdr = hdr.nexthdr;
  		len -= hdrlen;
  		start += hdrlen;
  	}
  
  	if (len < 0)
  		return -1;
  
  	*prevhdrp = prevhdr;
  	*prevhoff = prev_nhoff;
  	*fhoff = start;
  
  	return 0;
  }
  
  int nf_ct_frag6_gather(struct net *net, struct sk_buff *skb, u32 user)
  {
  	u16 savethdr = skb->transport_header;
  	int fhoff, nhoff, ret;
  	struct frag_hdr *fhdr;
  	struct frag_queue *fq;
  	struct ipv6hdr *hdr;
  	u8 prevhdr;
  
  	/* Jumbo payload inhibits frag. header */
  	if (ipv6_hdr(skb)->payload_len == 0) {
  		pr_debug("payload len = 0\n");
  		return 0;
  	}
  
  	if (find_prev_fhdr(skb, &prevhdr, &nhoff, &fhoff) < 0)
  		return 0;
  
  	if (!pskb_may_pull(skb, fhoff + sizeof(*fhdr)))
  		return -ENOMEM;
  
  	skb_set_transport_header(skb, fhoff);
  	hdr = ipv6_hdr(skb);
  	fhdr = (struct frag_hdr *)skb_transport_header(skb);
  
  	skb_orphan(skb);
  	fq = fq_find(net, fhdr->identification, user, hdr,
  		     skb->dev ? skb->dev->ifindex : 0);
  	if (fq == NULL) {
  		pr_debug("Can't find and can't create new queue\n");
  		return -ENOMEM;
  	}
  
  	spin_lock_bh(&fq->q.lock);
  
  	ret = nf_ct_frag6_queue(fq, skb, fhdr, nhoff);
  	if (ret == -EPROTO) {
  		skb->transport_header = savethdr;
  		ret = 0;
  	}
  
  	spin_unlock_bh(&fq->q.lock);
  	inet_frag_put(&fq->q);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(nf_ct_frag6_gather);
  
  static int nf_ct_net_init(struct net *net)
  {
  	int res;
  
  	net->nf_frag.frags.high_thresh = IPV6_FRAG_HIGH_THRESH;
  	net->nf_frag.frags.low_thresh = IPV6_FRAG_LOW_THRESH;
  	net->nf_frag.frags.timeout = IPV6_FRAG_TIMEOUT;
  	net->nf_frag.frags.f = &nf_frags;
  
  	res = inet_frags_init_net(&net->nf_frag.frags);
  	if (res < 0)
  		return res;
  	res = nf_ct_frag6_sysctl_register(net);
  	if (res < 0)
  		inet_frags_exit_net(&net->nf_frag.frags);
  	return res;
  }
  
  static void nf_ct_net_exit(struct net *net)
  {
  	nf_ct_frags6_sysctl_unregister(net);
  	inet_frags_exit_net(&net->nf_frag.frags);
  }
  
  static struct pernet_operations nf_ct_net_ops = {
  	.init = nf_ct_net_init,
  	.exit = nf_ct_net_exit,
  };
  
  static const struct rhashtable_params nfct_rhash_params = {
  	.head_offset		= offsetof(struct inet_frag_queue, node),
  	.hashfn			= ip6frag_key_hashfn,
  	.obj_hashfn		= ip6frag_obj_hashfn,
  	.obj_cmpfn		= ip6frag_obj_cmpfn,
  	.automatic_shrinking	= true,
  };
  
  int nf_ct_frag6_init(void)
  {
  	int ret = 0;
  
  	nf_frags.constructor = ip6frag_init;
  	nf_frags.destructor = NULL;
  	nf_frags.qsize = sizeof(struct frag_queue);
  	nf_frags.frag_expire = nf_ct_frag6_expire;
  	nf_frags.frags_cache_name = nf_frags_cache_name;
  	nf_frags.rhash_params = nfct_rhash_params;
  	ret = inet_frags_init(&nf_frags);
  	if (ret)
  		goto out;
  	ret = register_pernet_subsys(&nf_ct_net_ops);
  	if (ret)
  		inet_frags_fini(&nf_frags);
  
  out:
  	return ret;
  }
  
  void nf_ct_frag6_cleanup(void)
  {
  	unregister_pernet_subsys(&nf_ct_net_ops);
  	inet_frags_fini(&nf_frags);
  }
  